The objective of this ongoing research project is to evaluate a number of basic issues and assumptions underlying the clinical application of biofeedback techniques. A series of experiments is being conducted which focus on the two major biofeedback modalities in use today. The overall goals of these studies are to: (a) develop statistical criteria which are adequate to define physiological learning in the self-regulation of muscle and skin temperature activity; (b) evaluate the influence of placebo and expectational factors under double-blind experimental conditions; and (c) assess the human ability to volitionally self-regulate physiological activity under normal compared to stress avoidance conditions. To date, a viable procedure for presenting biofeedback training under truly double-blind conditions has been developed and successfully tested. Both group and individual physiological learning criteria have been developed. These criteria were successfully applied to differentiate EMG learning under contingent (real) biofeedback conditions compared to noncontingent (placebo) and motivated relaxation (no biofeedback) conditions. Finally, the "key muscle" hypothesis which underlies the therapeutic application of EMG biofeedback for reduction of generalized stress and anxiety, has been evaluated under rigorous laboratory conditions. Studies focusing on skin temperature self-regulation are now in progress.